Base station and radio terminal for performing radio access network paging

ABSTRACT

A user equipment and apparatus receive from a base station, configuration information configuring the user equipment to provide assistance information indicating a preference of the user equipment to leave RRC connected state, and transmit to the base station, assistance information indicating that a preferred RRC state of the user equipment is an RRC state in which an RRC connection is suspended. A base station transmits to a user equipment, configuration information configuring the user equipment to provide assistance information indicating a preference of the user equipment to leave RRC connected state, and receives from the user equipment, assistance information indicating that a preferred RRC state of the user equipment is an RRC state in which an RRC connection is suspended.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Continuation Application of U.S. patentapplication Ser. No. 16/901,773, filed Jun. 15, 2020, which is aContinuation Application of U.S. patent application Ser. No. 16/357,535,filed Mar. 19, 2019, which is a Continuation Application ofInternational Application No. PCT/JP2017/034053, filed Sep. 21, 2017,which claims the benefit of U.S. Provisional Application No. 62/397,453,filed Sep. 21, 2016, the entire contents of which are incorporatedherein by reference.

TECHNICAL FIELD

The present disclosure relates to a base station and a radio terminalthat are used in a mobile communication system.

BACKGROUND ART

In recent years, with the spread of radio terminals such as smartphonescapable of executing a lot of applications, the frequency at which aradio terminal connects to a network and the frequency at which anetwork performs paging of a radio terminal are increasing.

Therefore, in a mobile communication system, network load accompanyingsignaling is increasing. In view of such a situation, techniques forreducing signaling are being studied in the 3rd Generation PartnershipProject (3GPP), which is the standardization project for mobilecommunication systems.

SUMMARY OF DISCLOSURE

A user equipment according to the present disclosure comprises aprocessor and a memory. The processor is configured to receive from abase station, configuration information configuring the user equipmentto provide assistance information indicating a preference of the userequipment to leave RRC connected state, and transmit to the basestation, assistance information indicating that a preferred RRC state ofthe user equipment is an RRC state in which an RRC connection issuspended.

An apparatus according to the present invention for controlling a userequipment comprises a processor and a memory. The processor isconfigured to receive from a base station, configuration informationconfiguring the user equipment to provide assistance informationindicating a preference of the user equipment to leave RRC connectedstate, and transmit to the base station, assistance informationindicating that a preferred RRC state of the user equipment is an RRCstate in which an RRC connection is suspended.

A base station according to the present invention comprises a processorand a memory. The processor is configured to transmit to a userequipment, configuration information configuring the user equipment toprovide assistance information indicating a preference of the userequipment to leave RRC connected state, and receive from the userequipment, assistance information indicating that a preferred RRC stateof the user equipment is an RRC state in which an RRC connection issuspended.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating an architecture of an LTE systemaccording to an embodiment.

FIG. 2 is a diagram illustrating an architecture of a UE (radioterminal) according to an embodiment.

FIG. 3 is a diagram illustrating an architecture of an eNB (basestation) according to an embodiment.

FIG. 4 is a diagram illustrating an architecture of a protocol stack ofa radio interface in an LTE system according to an embodiment.

FIG. 5 is a diagram illustrating an architecture of a radio frame usedin an LTE system according to an embodiment.

FIG. 6 is a diagram illustrating an overview of an operation related toa transition to a light connected state (specific state) according to anembodiment.

FIG. 7 is a diagram illustrating an operation pattern 1 of anembodiment.

FIG. 8 is a diagram illustrating an operation pattern 2 of anembodiment.

FIG. 9 is a diagram illustrating an operation for determining a RANpaging area according to an embodiment.

FIG. 10 is a diagram illustrating an operation example according to afirst embodiment.

FIG. 11 is a diagram illustrating an operation example according to asecond embodiment.

FIG. 12 is a diagram illustrating an operation according to a thirdembodiment.

FIG. 13 is a diagram illustrating an operation pattern 1 of a fourthembodiment.

FIG. 14 is a diagram illustrating an operation pattern 2 of a fourthembodiment.

FIGS. 15A to 15C are diagrams illustrating operation examples accordingto a fifth embodiment.

DESCRIPTION OF EMBODIMENTS

[Mobile Communication System]

(Architecture of Mobile Communication System)

Hereinafter, an architecture of a mobile communication system accordingto an embodiment will be described. FIG. 1 is a diagram illustrating anarchitecture of a Long Term Evolution (LTE) system that is the mobilecommunication system according to an embodiment. The LTE system is amobile communication system based on the 3GPP standard.

As illustrated in FIG. 1, the LTE system includes a radio terminal (userequipment (UE)) 100, a radio access network (evolved-UMTS terrestrialradio access network (E-UTRAN)) 10, and an evolved packet core (EPC) 20.

The UE 100 is a mobile communication apparatus and performs radiocommunication with an eNB 200 that manages a cell (serving cell) inwhich the UE 100 exists.

The E-UTRAN 10 includes a base station (evolved Node-B (eNB)) 200. TheeNBs 200 are connected to each other via an X2 interface. The eNB 200manages one or more cells and performs radio communication with the UE100 that has established connection to the cell. The eNB 200 has a radioresource management (RRM) function, a user data (hereinafter, simplyreferred to as “data”) routing function, a measurement control functionfor mobility control and scheduling, and the like. The “cell” is used asthe term indicating the smallest unit of the radio communication areaand is also used as the term indicating the function or resource ofperforming radio communication with the UE 100.

The EPC 20 includes a mobility management entity (MME) 300C and aserving gateway (S-GW) 300U (see FIG. 6 or the like). The MME 300Cperforms various types of mobility control or the like on the UE 100.The MME 300C communicates with the UE 100 by using non-access stratum(NAS) signaling to manage information of a tracking area (TA) in whichthe UE 100 exists. The tracking area is an area provided with aplurality of cells. The S-GW 300U performs data transfer control. TheMME 300C and the S-GW 300U are connected to the eNB 200 via an S1interface.

FIG. 2 is a diagram illustrating the architecture of the UE 100 (radioterminal). As illustrated in FIG. 2, the UE 100 includes a receiver 110,a transmitter 120, and a controller 130.

The receiver 110 performs a variety of reception under the control ofthe controller 130. The receiver 110 includes an antenna and a receivingmachine. The receiving machine converts a radio signal received by theantenna into a baseband signal (reception signal) and outputs thebaseband signal to the controller 130.

The transmitter 120 performs a variety of transmission under the controlof the controller 130. The transmitter 120 includes an antenna and atransmitting machine. The transmitting machine converts a basebandsignal (transmission signal) output by the controller 130 into a radiosignal and transmits the radio signal from the antenna.

The controller 130 performs a variety of control on the UE 100. Thecontroller 130 includes at least one processor and a memory. The memorystores a program executed by the processor and information used forprocessing by the processor. The processor may include a basebandprocessor that performs modulation and demodulation, coding anddecoding, and the like of the baseband signal, and a central processingunit (CPU) that performs a variety of processes by executing a programstored in the memory. The processor performs a process to be describedlater.

FIG. 3 is a diagram illustrating the architecture of the eNB 200 (basestation). As illustrated in FIG. 3, the eNB 200 includes a transmitter210, a receiver 220, a controller 230, and a backhaul communication unit240.

The transmitter 210 performs a variety of transmission under the controlof the controller 230. The transmitter 210 includes an antenna and atransmitting machine. The transmitting machine converts a basebandsignal (transmission signal) output by the controller 230 into a radiosignal and transmits the radio signal from the antenna.

The receiver 220 performs a variety of reception under the control ofthe controller 230. The receiver 220 includes an antenna and a receivingmachine. The receiving machine converts a radio signal received by theantenna into a baseband signal (reception signal) and outputs thebaseband signal to the controller 230.

The controller 230 performs a variety of control on the eNB 200. Thecontroller 230 includes at least one processor and a memory. The memorystores a program executed by the processor and information used forprocessing by the processor. The processor may include a basebandprocessor that performs modulation and demodulation, coding anddecoding, and the like of the baseband signal, and a CPU that performs avariety of processes by executing a program stored in the memory. Theprocessor performs a process to be described later.

The backhaul communication unit 240 is connected to the neighbor eNB viaan X2 interface and connected to the MME/S-GW 300 via an S1 interface.The backhaul communication unit 240 is used for communication performedon the X2 interface, communication performed on the S1 interface, andthe like.

It should be noted that the MME 300C includes a controller and a networkcommunication unit. The controller performs a variety of control on theMME 300C.

The controller includes at least one processor and a memory. The memorystores a program executed by the processor and information used forprocessing by the processor. The processor may include a basebandprocessor that performs modulation and demodulation, coding anddecoding, and the like of the baseband signal, and a CPU that performs avariety of processes by executing a program stored in the memory. Theprocessor performs a process to be described later. The networkcommunication unit is connected to the eNB 200 via an S1 interface. Thenetwork communication unit is used for communication or the likeperformed on the S1 interface.

FIG. 4 is a diagram illustrating the architecture of the protocol stackof the radio interface in the LTE system. As illustrated in FIG. 4, aradio interface protocol is divided into a first layer to a third layerof an OSI reference model, and the first layer is a physical (PHY)layer. The second layer includes a medium access control (MAC) layer, aradio link control (RLC) layer, and a packet data convergence protocol(PDCP) layer. The third layer includes a radio resource control (RRC)layer. The PHY layer, the MAC layer, the RLC layer, the PDCP layer, andthe RRC layer constitute an access stratum (AS) layer.

The PHY layer performs coding and decoding, modulation and demodulation,antenna mapping and demapping, and resource mapping and demapping. Dataand control information are transmitted between the PHY layer of the UE100 and the PHY layer of the eNB 200 via a physical channel.

The MAC layer performs priority control of data, a retransmissionprocess by hybrid ARQ (HARQ), a random access procedure, and the like.Data and control information are transmitted between the MAC layer ofthe UE 100 and the MAC layer of the eNB 200 via a transport channel. TheMAC layer of the eNB 200 includes a scheduler that determines uplink anddownlink transport formats (transport block size, modulation and codingscheme (MCS)) and resource blocks allocated to the UE 100.

The RLC layer transmits data to the RLC layer on the receiving side byusing the functions of the MAC layer and the PHY layer. Data and controlinformation are transmitted between the RLC layer of the UE 100 and theRLC layer of the eNB 200 via a logical channel.

The PDCP layer performs header compression and decompression, andencryption and decryption.

The RRC layer is defined only in a control plane that handles thecontrol information. RRC signaling for various configurations istransmitted between the RRC layer of the UE 100 and the RRC layer of theeNB 200. The RRC layer controls logical channels, transport channels,and physical channels in response to establishment, re-establishment,and release of radio bearers. If there is a connection (RRC connection)between the RRC of the UE 100 and the RRC of the eNB 200, the UE 100 isin an RRC connected mode; otherwise, the UE 100 is in an RRC idle mode.

A NAS layer, which is located above the RRC layer, performs sessionmanagement, mobility management, and the like. NAS signaling istransmitted between the NAS layer of the UE 100 and the NAS layer of theMME 300C. It should be noted that the UE 100 has a function such as anapplication layer in addition to the protocol of the radio interface.

FIG. 5 is a diagram illustrating the architecture of the radio frameused in the LTE system. As illustrated in FIG. 5, the radio frameincludes ten subframes on a time axis. Each subframe includes two slotson the time axis. A length of each subframe is 1 ms, and a length ofeach slot is 0.5 ms. Each subframe includes a plurality of resourceblocks (RB) on a frequency axis and includes a plurality of symbols on atime axis. Each resource block includes a plurality of subcarriers onthe frequency axis. Specifically, one RB is constituted by twelvesubcarriers and one slot. One symbol and one subcarrier constitute oneresource element (RE). In addition, among the radio resources (time andfrequency resources) allocated to the UE 100, the frequency resource canbe specified by the resource block and the time resource can bespecified by the subframe (or slot).

In the downlink, a section of several symbols in the head of eachsubframe is a region that is mainly used as a physical downlink controlchannel (PDCCH) for transmitting downlink control information. Inaddition, the remaining portion of each subframe is a region that ismainly used as a physical downlink shared channel (PDSCH) fortransmitting downlink data.

Basically, the eNB 200 transmits downlink control information (DCI) tothe UE 100 by using the PDCCH and transmits downlink data to the UE 100by using the PDSCH. The DCI carried by the PDCCH includes uplinkscheduling information, downlink scheduling information, and a TPCcommand. The uplink scheduling information is scheduling information (ULgrant) about allocation of uplink radio resources, and the downlinkscheduling information is scheduling information related to allocationof downlink radio resources. The TPC command is information instructingincrease or decrease of uplink transmission power. The eNB 200 includesa CRC bit scrambled with an identifier (RNTI: radio network temporaryID) of the destination UE 100 in the DCI so as to identify the UE 100that is the transmission destination of the DCI. Each UE 100 performsblind decoding on the PDCCH by performing CRC check after descramblingwith the RNTI of the UE in the DCI that may be addressed to the UE, anddetects the DCI addressed to the UE. The PDSCH carries downlink data bythe downlink radio resource (resource block) indicated by the downlinkscheduling information.

In the uplink, both end portions in the frequency direction in eachsubframe is a region that is mainly used as a physical uplink controlchannel (PUCCH) for transmitting uplink control information. Theremaining portion of each subframe is a region that is mainly used as aphysical uplink shared channel (PUSCH) for transmitting uplink data.

Basically, the UE 100 transmits uplink control information (UCI) to theeNB 200 by using the PUCCH and transmits uplink data to the eNB 200 byusing the PUSCH. The UCI carried by the PUCCH includes a channel qualityindicator (CQI), a precoding matrix indicator (PMI), a rank indicator(RI), a scheduling request (SR), and HARQ ACK/NACK. The CQI is an indexindicating downlink channel quality and is used for determining the MCSto be used for downlink transmission or the like. The PMI is an indexindicating a precoder matrix that is preferably used for downlinktransmission. The RI is an index indicating the number of layers (numberof streams) that can be used for downlink transmission. The SR isinformation requesting allocation of PUSCH resources. The HARQ ACK/NACKis delivery confirmation information indicating whether the downlinkdata has been correctly received.

(Specific State)

Hereinafter, a specific state according to an embodiment will bedescribed. The specific state is a state in which the signaling for theUE 100 is suppressed while an S1 connection for the UE 100 ismaintained. The S1 connection may be referred to as an S1 bearer. The S1connection is a connection established between the eNB 200 and the EPC20 on the S1 interface. The S1 interface includes an S1-U interface fora user plane and an S1-MME interface for a control plane. The S1connection includes an S1-U connection established between the eNB 200and the S-GW 300U on the S1-U interface, an S1-MME connectionestablished between the eNB 200 and the MME 300C on the S1-C interface.

The specific state may be one state of an RRC connected mode or onestate of an RRC idle mode. Alternatively, the specific state may be anRRC idle mode and an RRC state different from the RRC idle mode. In anoperation pattern 1 of an embodiment, the specific state is one state(substate) of the RRC connected mode. On the other hand, in an operationpattern 2 of an embodiment, the specific state is one state (substate)of the RRC connected mode. According to the specific state, signaling isreduced as compared with a general RRC connected mode. In addition,according to the specific state, the UE 100 can start data communicationquickly, as compared with a general RRC idle mode. Hereinafter, thespecific state is referred to as “light connected state (light connectedsubstate)”.

FIG. 6 is a diagram illustrating an overview of an operation related toa transition to a light connected state (specific state). In an initialstate of FIG. 6, the UE 100 is in an RRC connected mode, and an RRCconnection is established between the UE 100 and the eNB 200. Inaddition, an S1-MME connection is established between the eNB 200 andthe MME 300C. An S1-U connection is established between the eNB 200 andthe S-GW 300U. The UE 100 performs data communication with the eNB 200.

As illustrated in FIG. 6, in step S1, the eNB 200 transmits, to the UE100, a transition instruction (Request to Light Conn.) instructing atransition to the light connected state.

In step S2, the UE 100 transmits an acknowledgment (Ack) message to theeNB 200 in response to reception of the transition instruction. However,step S2 is not essential and can be omitted.

In step S3, the UE 100 and the eNB 200 maintain or release the RRCconnection. Specifically, in the operation pattern 1 of the embodiment,the UE 100 and the eNB 200 maintain the RRC connection. On the otherhand, in the operation pattern 2 of the embodiment, the UE 100 and theeNB 200 release the RRC connection.

In step S4, the eNB 200 and the MME 300C maintain the S1-MME connection.In step S5, the eNB 200 and the S-GW 300U maintain the S1-U connection.In step S6, the UE 100 transitions to the light connected state andsuspends data communication with the eNB 200.

The eNB 200 maintains context information (UE context) of the UE 100that has transitioned to the light connected state, without discardingthe context information. The UE context includes information related tovarious configurations and capabilities for the UE 100. The variousconfigurations include a configuration of access stratum (AS).

The UE 100 in the light connected state can resume data communicationwith the eNB 200 with less signaling by using the maintained S1connection and UE context.

The UE 100 that has transitioned to the light connected state in thecell of the first eNB 200 may move from the cell of the first eNB 200 tothe cell of the second eNB 200. If the UE 100 resumes data communicationin the cell of the second eNB 200, the second eNB 200 acquires the UEcontext of the UE 100 on the X2 interface from the first eNB 200 anduses the acquired UE context for data communication with the UE 100.

In an embodiment, RAN paging is applied to the UE 100 in the lightconnected state. RAN paging performs paging in units of predeterminedpaging areas in which paging is controlled by the E-UTRAN 10 (eNB 200).The predetermined paging area is an area narrower than the trackingarea. By introducing a predetermined paging area, it is possible toreduce the number of cells that perform paging on one UE 100, therebyreducing signaling. Hereinafter, such a predetermined paging area willbe referred to as an “RAN paging area”.

As an example, the RAN paging area (predetermined paging area) isconstituted by the cell of the specific eNB 200 maintaining the S1connection of the UE 100 in the light connected state and the cell ofthe eNB 200 around the specific eNB 200. The neighbor eNB 200 may be aneNB 200 having an X2 interface with the specific eNB 200. If the NASsignaling or data addressed to the UE 100 in the light connected stateis received from the MME/S-GW 300, the specific eNB 200 determines thatRAN paging is to be performed, and the UE 100 performs paging togetherwith the neighbor eNB 200. The paging may be performed by transmittingan RRC paging message, or may be performed by transmitting dataaddressed to the UE 100 as a paging message. The specific eNB 200 may bereferred to as an anchor eNB.

(Operation Pattern 1) Hereinafter, an operation pattern 1 of anembodiment will be described.

In the operation pattern 1, the UE 100 in the RRC connected modereceives, from the eNB 200, a message instructing the configurationchange of the RRC connection, and changes the configuration according tothe reception of the message. As an example, the message is an RRCconnection reconfiguration message. As another example, the message is amessage different from the RRC connection reconfiguration message. Inthe operation pattern 1, a case in which the message is the RRCconnection reconfiguration message is assumed. The eNB 200 changes theRRC configuration of the UE 100 by transmitting the RRC connectionreconfiguration message to the UE 100.

The eNB 200 transitions the UE 100 to the light connected state byincluding information instructing the transition to the light connectedstate in the RRC connection reconfiguration message. The UE 100transitions to the light connected state in response to the fact thatthe information instructing the transition to the light connected stateis included in the RRC connection reconfiguration message. In theoperation pattern 1, the light connected state is a state in which atleast one function for generating signaling with the eNB 200 among aplurality of functions of the UE 100 is deactivated while maintainingthe RRC connection.

Here, the plurality of functions (features) may include a data (userdata) transceiving function, a scheduling request (SR) transmittingfunction, a channel state information (CSI) transmitting (that is, CSIfeedback) function, a sounding reference signal (SRS) transmittingfunction, a carrier aggregation function, a dual connectivity function,a semi-persistent scheduling (SPS) function, a WLAN aggregationfunction, a radio link monitoring (RLM) function, a notification(in-device coexistence indication UE assistance information, MBMSinterest indicator, sidelink UE information, etc) function, an idle modediscontinuous reception (DRX) function, and a WLAN interwork functionusing broadcast signaling. However, in the light connected state, atleast one of the cell reselection function, a connected mode DRXfunction, and the WLAN interworking function using dedicated signalingmay be maintained in an activated state without being deactivated. Fordetails of these functions, see, for example, 3GPP technicalspecification “TS 36.300 V 13.4.0”.

FIG. 7 is a diagram illustrating the operation pattern 1 of theembodiment. In the initial state of FIG. 7, the UE 100 is in the RRCconnected mode and performs data communication with the eNB 200. Itshould be noted that the process indicated by the dashed line in FIG. 7is not essential and can be omitted.

As illustrated in FIG. 7, in step S101, the UE 100 detects interruptionof data communication with the eNB 200.

The interruption of the data communication may include a case in whichdownlink (DL) data is not received (or it is unlikely to receivedownlink (DL) data) and/or a case in which uplink (UL) data is nottransmitted (or it is unlikely to transmit uplink (UL) data). Here, thelikelihood may be a state in which it is predicted that data will not begenerated in a certain period. The predetermined period may beconfigured from the eNB 200. The configuration from the eNB 200 to theUE 100 is performed by RRC signaling. The RRC signaling may be aUE-dedicated signaling (for example, an RRC connection reconfigurationmessage) or a broadcast signaling (for example, a system informationblock (SIB)).

As an example, the RRC layer of the UE 100 detects interruption of datacommunication with the eNB 200 based on information of a layer (forexample, application layer) higher than the RRC layer. As an example,the RRC layer of the UE 100 may detect interruption of datacommunication in response to shutdown of an application with the highestcommunication frequency at the present time. As another example, the RRClayer of the UE 100 may detect interruption of data communication inresponse to the fact that the operation system (OS) makes communicationrestrictions, the fact that there are no applications running in theforeground (that is, there is only the background process), and the factthat the OS determines that the data communication is interrupted.

In step S102, the UE 100 transmits, to the eNB 200, a notificationindicating that the data communication is interrupted. The UE 100 maytransmit the notification by signaling of the RRC layer. The signalingof the RRC layer may be a UE assistance information message or anothermessage. If the notification indicating the interruption of the datacommunication is transmitted in the UE assistance information message,the notification may be referred to as an extended power preferenceindicator (extended PPI).

In step S103, the eNB 200 determines to make the UE 100 transition tothe light connected state in response to reception of the notificationindicating the interruption of the data communication.

In step S104, the eNB 200 transmits, to the UE 100, an RRC connectionreconfiguration message (or another message) including informationinstructing a transition to the light connected state. In other words,the eNB 200 transmits the instruction of the transition to the lightconnected state as the configuration change of the RRC connection.

The information instructing the transition to the light connected stateis, for example, “Light Connected=Setup”. In addition, the RRCconnection reconfiguration message may include information designating adeactivation function among the plurality of functions described above.As an example, the eNB 200 includes a list of activation maintenancefunctions or a list of deactivation functions in the RRC connectionreconfiguration message in order to individually designate functions tobe deactivated.

In step S105, the UE 100 deactivates a predetermined function among theplurality of functions (features) described above in response to thereception of the RRC connection reconfiguration message including theinformation instructing the transition to the light connected state. Ifthe deactivated function is designated by the RRC connectionreconfiguration message, the UE 100 deactivates only the designatedfunction.

In step S106, the UE 100 holds the configuration information (AScontext) of the predetermined function even if the predeterminedfunction is deactivated. In other words, even if transitioning to thelight connected state, the UE 100 maintains the configurationinformation of the deactivated function without discarding thedeactivating function.

In step S107, the UE 100 transitions to the light connected state. Inthe operation pattern 1, the light connected state is one state(substate) of the RRC connected mode. The UE 100 in the light connectedstate performs a process for receiving a paging message transmittedwithin an RAN paging area.

After that, in step S108, the UE 100 in the light connected statedetects a predetermined event in the UE 100. The predetermined event iseither the reception of the paging message from the eNB 200 or theoccurrence of the UL data to be transmitted to the eNB 200. Thepredetermined event may be that the UL data is generated and the amountof the UL data is equal to or greater than a threshold value. Thethreshold value may be configured to the UE 100 from the eNB 200.

In step S109, the UE 100 in the light connected state transmits, to theeNB 200, an activation request (RRC activation request) requesting theactivation of the deactivated function in response to the detection ofthe predetermined event.

The activation request may require the activation of all the deactivatedfunctions or may require the activation of some deactivated functions.In the case of requesting the activation of all the deactivatedfunctions, the activation request may be a stop request of the lightconnected state (that is, a transition request to a normal RRC connectedmode). On the other hand, in the case of requesting the activation ofall the deactivated functions, the activation request may include a listof functions to be activated, or may include a list of functions tomaintain a deactivated state.

In step S110, in response to the reception of the activation request,the eNB 200 determines whether the request is acceptable. Here, thedescription will be given on the assumption that the eNB 200 determinesthat the request is acceptable. It should be noted that if the eNB 200determines that the request is not acceptable, the eNB 200 may transmita non-acknowledgment (Nack) or a rejection notification (Reject) to theUE 100.

In step S111, the eNB 200 transmits, to the UE 100, an acknowledgment(RRC activation acknowledge) to the activation request. It should benoted that the eNB 200 may determine whether to accept the activationrequest for each function. In this case, the eNB 200 may include, in theRRC activation acknowledge, a list of functions that permit activationand/or a list of functions that reject activation. Alternatively,instead of the acknowledgment, an RRC connection reconfiguration messagemay be used.

In step S112, the UE 100 determines whether to activate the deactivatedfunction based on the contents of the response received from the eNB200. If the acknowledgment is received, the UE 100 activates thepermitted function. The UE 100 activates the function from the timepoint (subframe) when the acknowledgment is received. Alternatively, theUE 100 may activate the function within a certain period (for example,within eight subframes) after the acknowledgment is received.

(Operation Pattern 2) In the operation pattern 2 of the embodiment, adifference from the operation pattern 1 will be mainly described below.

In the operation pattern 2, the UE 100 in the RRC connected modereceives, from the eNB 200, an RRC connection release messageinstructing the release of the RRC connection, and releases the RRCconnection in response to the reception of the RRC connection releasemessage. The RRC connection release message includes a field (releasecause) indicating the cause of releasing the RRC connection. The UE 100transitions to the light connected state in response to the fact thatthe field includes information (for example, RRC-LightConnected)instructing the transition to the light connected state is included inthe field. The eNB 200 transitions the UE 100 to the light connectedstate by including the information instructing the transition to thelight connected state in the field. Alternatively, the light connectedstate may be one state in the network (that is, the eNB and theMME/S-GW). In this case, the RRC state of UE 100 is idle. However, theeNB 200 may cause the UE to hold the context (configurationinformation). In this case, the eNB 200 configures the release cause ofthe RRC connection release to rrc-Suspend, and notifies the UE 100 ofresume ID (resumeldentity) that is an identifier corresponding thereto.The state may be referred to as a state in which the RRC connection issuspended.

In the operation pattern 2, the light connected state is a state inwhich the RRC connection is released and the S1 connection for the UE100 is maintained between the eNB 200 and the core network (EPC 20). Inthe operation pattern 2, the light connected state may be further astate in which at least a part of the plurality of functions describedabove is deactivated.

FIG. 8 is a diagram illustrating the operation pattern 2 of theembodiment. In the following, a difference from the operation pattern 1illustrated in FIG. 7 will be mainly described and a redundantdescription thereof will be omitted.

As illustrated in FIG. 8, steps S201 to S203 are similar to theoperation pattern 1.

In step S204, the eNB 200 transmits, to the UE 100, an RRC connectionrelease message including information instructing a transition to alight connected state as a release cause. The RRC connection releasemessage may include information designating a deactivating functionamong the plurality of functions described above. In this case, thehandling of the deactivating function is the same as the operationpattern 1. The RRC connection release message may include a resumeidentifier (resume ID). The eNB 200 holds the UE context in associationwith the resume identifier.

In step S205, the UE 100 releases the RRC connection with the eNB 200 inresponse to the reception of the RRC connection release messageincluding the information instructing the transition to the lightconnected state as the release cause.

In step S206, the UE 100 transitions to the light connected state. Inthe operation pattern 2, the light connected state is one state(substate) of the RRC idle mode. The UE 100 in the light connected stateperforms a process for receiving a paging message transmitted within anRAN paging area.

After that, in step S207, the UE 100 in the light connected statedetects a predetermined event in the UE 100.

In step S208, the UE 100 in the light connected state transmits, to theeNB 200, an RRC connection resume request requesting the resume of theRRC connection in response to the detection of the predetermined event.The RRC connection resume request may include information requesting theactivation of the deactivated function. The RRC connection resumerequest may include a resume identifier.

In step S209, in response to the reception of the RRC connection resumerequest, the eNB 200 determines whether the request is acceptable. Here,the description will be given on the assumption that the eNB 200determines that the request is acceptable.

In step S210, the eNB 200 transmits an RRC connection resume message tothe UE 100. The eNB 200 may include, in the RRC connection resumemessage, a list of functions that permit activation and/or functionsthat reject activation.

In step S211, the UE 100 resumes the RRC connection based on the RRCconnection resume message received from the eNB 200. The eNB 200 resumesthe use of the UE context based on the resume identifier.

(Mobility Status Information) In the operation patterns 1 and 2, thenotification indicating interruption of data communication may includemobility status information related to the moving speed of the UE 100.The eNB 200 receives the mobility status information related to themoving speed of the UE 100 from the UE 100 and determines the range ofthe RAN paging area corresponding to the UE 100 based on the mobilitystatus information.

Alternatively, the UE 100 may transmit the mobility status informationto the eNB 200 at any of the following timings.

First, the UE 100 transmits the mobility status information with theupdate of the tracking area or the RAN paging area as a trigger. In thiscase, the UE 100 may include the mobility status information in atracking area update message or a RAN paging area update message.

Second, the UE 100 transmits mobility status information with the cellreselection as a trigger. In this case, the UE 100 may include themobility status information in the cell update message.

Third, the UE 100 transmits the mobility status information with aninquiry from the eNB 200 as a trigger.

Fourth, the UE 100 periodically transmits the mobility statusinformation. The period may be configured from the eNB 200 to the UE100.

FIG. 9 is a diagram illustrating the operation for determining the RANpaging area.

As illustrated in FIG. 9, in step S301, the UE 100 generates mobilitystatus information. The mobility status information includes at leastone piece of the following information.

1) Number of times of handovers or number of times of cell reselectionswithin predetermined time. The predetermined time may be configured fromthe eNB 200 to the UE 100.

2) Average moving speed within predetermined time. The moving speed canbe obtained from position information of the UE 100. The moving speed isnot limited to a value of a direct moving speed (for example, xxx km/h)and may be an index of a moving speed (for example, high/mid/low). Thepredetermined time may be configured from the eNB 200 to the UE 100.

3) 1-bit identifier indicating whether moving speed exceeds thresholdvalue. Here, the above 1) or 2) can be used as the moving speed. Thethreshold value may be configured from the eNB 200 to the UE 100.

4) Cell history information of UE 100. The cell history informationincludes a plurality of combinations of the ID of the cell and thestaying time in the cell.

In step S302, the UE 100 transmits, to the eNB 200, a message includingthe mobility status information. The UE 100 may further include its ownposition information in the message. The UE 100 may further include itsown category (UE category) in the message.

In step S303, the eNB 200 decides the range of the RAN paging area basedon the mobility status information. The eNB 200 may notify the MME 300Cof the list of cells (and eNBs) belonging to the determined RAN pagingarea.

As an example, the eNB 200 configures a wider RAN paging area to the UE100 having a high moving speed so as to prevent missed paging. On theother hand, a narrower RAN paging area is configured to the UE 100 witha slow moving speed so as to reduce the number of signalings by thepaging message.

As another example, the eNB 200 configures a wider RAN paging area tothe UE 100 of a category M1 so as to reduce power consumption. Thecategory M1 is a UE category for machine type communication and requiresa power saving operation. This makes it possible to reduce the RANpaging area update message required when leaving the RAN paging area.

First Embodiment

Hereinafter, the first embodiment will be described on the premise ofthe above-described LTE system. The first embodiment is an embodimentrelating to the mobility in the light connected state.

Here, the basic operation of the mobility in the light connected statewill be described.

-   -   The S1 connection of the UE 100 in the light connected state is        maintained at “anchor eNB” and is active. The anchor eNB may be        an eNB 200 that has transitioned the UE 100 to the light        connected state. If the UE 100 moves to another RAN paging area,        the anchor eNB may be switched.    -   Paging (RAN paging) can be performed with the RAN (E-UTRAN 10)        startup with respect to the UE 100 in the light connected state.        The RAN paging may be started by the anchor eNB.    -   Paging process (RAN paging) is controlled by the anchor eNB.    -   The RAN paging area can be configured to be UE-specific.    -   The UE 100 in the light connected state performs a cell        reselection mechanism similar to the RRC idle mode.    -   The context information (UE AS context) of the UE 100 in the        light connected state is held in both the UE and the anchor eNB.    -   From the viewpoint of the network, the light connected state is        an EPS connection management (ECM) connected state. The ECM        indicates a connection state between the UE 100 and the core        network (MME 300C).    -   If the UE 100 in the light connected state detects paging or        starts data transmission, the UE 100 resumes the connection with        the eNB 200. Alternatively, the UE 100 may transition to the RRC        connected mode.    -   The UE 100 transitions to the light connected state by RRC        signaling.    -   The UE-specific RAN paging area is configured from the eNB 200        to the UE 100 by dedicated signaling or broadcast signaling. The        RAN paging area is designated by a cell list or a paging area        ID.    -   If the UE 100 moves outside the configured RAN paging area, the        UE 100 in the light connected state notifies the network of the        fact.    -   The RAN paging area is constituted by one or more cells. The        plurality of cells may be managed by different eNBs.    -   The UE 100 in the light connected state performs the DRX        operation by using the same parameters as the DRX operation of        the RRC idle mode. The parameters for determining the paging        occasion may include the ID of the UE (for example, IMSI,        S-TMSI, resume ID, and the like).

The eNB 200 according to the first embodiment is the eNB 200 included inthe RAN of the mobile communication system. The eNB 200 includes areceiver 220 that receives, from the UE 100 in the light connectedstate, a message indicating that the UE 100 left the RAN paging area,and a transmitter (backhaul communication unit 240) that transmits, tothe MME 300C (mobility management entity), paging area informationrelated to the update of the RAN paging area in response to thereception of the message. The light connected state is a state in whichthe anchor eNB in the RAN paging area maintains the S1 connection forthe UE 100, and the RAN paging area is configured to the UE 100.

In the eNB 200 according to the first embodiment, the transmitter (thebackhaul communication unit 240) may transmit, to the MME 300C, a switchrequest message including the paging area information. The switchrequest message is a message for a request to switch the S1 connectionto the eNB 200.

In addition, the paging area information may include informationindicating a new RAN paging area for the UE 100. The new RAN paging areaincludes the area (cell) of the eNB 200.

FIG. 10 is a diagram illustrating the operation example according to thefirst embodiment. In the initial state of FIG. 10, the UE 100 is in theRRC connected mode (S1001). In addition, the connection state betweenthe UE 100 and the core network (MME 300C) is ECM connected, and the S1connection (S1-MME connection) for the UE 100 exists between the eNB 200and the MME 300C. Although not illustrated, the S1 connection (S1-Uconnection) for the UE 100 also exists between the eNB 200 and the S-GW300U.

As illustrated in FIG. 10, in step S1003, the anchor eNB 200-1transmits, to the UE 100, a transition instruction (light connectionInstruction) instructing the transition to the light connected state. Asdescribed above, the transition instruction is transmitted in the RRCconnection reconfiguration message or the RRC connection releasemessage. The anchor eNB 200-1 may configure, to the UE 100, the RANpaging area specific to the UE 100.

In step S1004, the UE 100 transitions to the light connected state inresponse to the reception of the transition instruction from the cell(serving cell) of the anchor eNB 200-1.

In step S1005, the UE 100 detects that the UE 100 has moved outside theRAN paging area configured to the UE 100 based on, for example, the cellidentifier, the paging area ID, or the like transmitted from the eNB200-2 outside the RAN paging area. It should be noted that the eNB 200-2may not have the X2 interface with the anchor eNB 200-1.

In step S1006, the UE 100 transmits, to the eNB 200-2, a messageindicating that the UE 100 has left the RAN paging area configured tothe UE 100. The message may be a message (paging area update) indicatingthe update of the RAN paging area. The message may be a message (RRCconnection boot request) requesting the resume from the light connectedstate. The message may be an RRC connection resume request message.

The message may include resume ID, short resume MAC-I, and resume cause.

Alternatively, instead of the resume ID, an identifier including acombination of a cell identifier (cell ID) and a cell-radio. Networktemporary identifier (C-RNTI) may be used. The cell ID may be an E-UTRANcell global identifier (ECGI), an E-UTRAN cell identifier (ECI), or aphysical cell identifier (PCI). The cell ID and/or the C-RNTI may not beexplicitly given as the instruction for the transition to the LightConnected (for example, RRC connection release). If the UE 100 receivesthe transition instruction to the Light Connected, the UE 100 may storethe cell ID of the cell and the currently allocated C-RNTI. Whenresuming, the UE 100 reads this value and notifies the value to the eNB200.

The ECGI includes a combination of an ECI and a PLMN ID. That is, theECI does not have a PLMN ID. Therefore, if the ECI is used as the cellidentifier, the identifier composed of the combination may be valid onlywithin the same public land mobile network (PLMN).

If the PCI is used as the cell identifier, the eNB 200 may discover thespecific eNB (anchor eNB) by using the PCI received from the UE 100 andthe neighbor list (neighbor relation table).

Whether the UE 100 should notify the identifier including the abovecombination may be designated from the eNB 200. For example, the eNB 200informs the SIB so as to notify the identifier composed of thecombination of the ECI and the C-RNTI. Alternatively, the eNB 200 may beconfigured individually for the UE 100.

In addition, although omitted in the drawing, even if the ECI and thePCI are used, since the eNB 200 can specify the specific eNB (anchoreNB), the eNB 200 can obtain UE context (configuration information) fromthe specific eNB by using the X2 or S1 interface.

Although not illustrated in the drawing, the identifier composed of thecombination may be used for specifying the calling UE in paging. If theUE 100 receives the paging message, the UE 100 reads the identifier, andif the identifier matches the identifier in the paging message, the UE100 determines that the UE 100 is called. In this case, the UE 100 maystart an operation of establishing an RRC connection (for example,transmitting an RRC connection request).

In addition, instead of the resume cause, boot cause related to theresume from Light Connected may be used. Alternatively, as the resumecause, a new value such as LightConnected-Access related to the resumefrom Light Connected may be defined.

In step S1007, in response to the reception of the message from the UE100, the eNB 200-2 transmits, to the MME 300C, a message (S1 path switchrequest) for requesting to switch the S1 connection to the eNB 200-2 onthe S1 interface. The message (S1 path switch request) includes the IDand address of the E-RAB that performs the path switch, the source MMEUE S1AP ID, the cell ID, and the like. The eNB 200-2 includes paginginformation (PA info.) indicating a new RAN paging area for the UE 100in the message (path switch request). The paging information (PA info.)may be a list of cells (recommended cell list) included in a new RANpaging area.

In step S1008, the MME 300C grasps or determines a new RAN paging areaof the UE 100 based on the message (path switch request) received fromthe eNB 200-2. That is, the MME 300C can manage the RAN paging area inwhich the UE 100 exists, based on the paging information (PA info.). Inaddition, the MME 300C performs a process of switching the S1 connectionfor the UE 100 from the anchor eNB 200-1 to the eNB 200-2.

In the present sequence, it is assumed that no X2 interface existsbetween the anchor eNB 200-1 and the eNB 200-2. However, if the X2interface exists between the anchor eNB 200-1 and the eNB 200-2, the eNB200-2 may transmit the UE context release or the UE context retrieve tothe anchor eNB 200-1 on the X2 interface in response to the reception ofthe message from the UE 100. The UE context release is a message forrequesting the release of the context information of the UE 100. The UEcontext retrieve is a message for acquiring the context information ofthe UE 100. The eNB 200-2 may include paging information (PA info.) inthese messages. The anchor eNB 200-1 may transfer, to the MME 300 C, thepaging information (PA info.) received from the eNB 200-2.

Second Embodiment

In a second embodiment, a difference from the first embodiment will bemainly described below. The second embodiment is an embodiment relatedto an operation in which the eNB 200 performs RAN paging.

The eNB 200 according to the second embodiment includes a controller 230that performs RAN paging on the UE 100 in the light connected state anddetermines whether the RAN paging is successful, and a transmitter(backhaul communication unit 240) that transmits, to the MME 300C, afailure notice indicating the failure of the RAN paging in response tothe failure of the RAN paging. The RAN paging is an operation in whichthe RAN performs paging of the UE 100 in units of RAN paging areas. Thefailure notice may be a message for causing the MME 300C to performpaging based on the tracking area in which the UE 100 exists. Therefore,even if the RAN paging fails, the MME 300C can perform normal paging.

The eNB 200 according to the second embodiment may include a receiver(backhaul communication unit 240) that receives, from another eNB 200,information related to whether the another eNB 200 in the RAN pagingarea has succeeded in paging. The controller 230 determines that the RANpaging has failed in response to the failure of the paging at both theeNB 200 and the another eNB 200.

FIG. 11 is a diagram illustrating the operation example according to thesecond embodiment. In FIG. 11, the anchor eNB 200-1 and the eNB 200-2belong to the same RAN paging area. The anchor eNB 200-1 and the eNB200-2 may be connected via the X2 interface. In the initial state ofFIG. 11, the UE 100 is in the RRC connected mode (S2001, S2002). Itshould be noted that the operation indicated by the broken line in FIG.11 is not essential.

As illustrated in FIG. 11, the operations of steps S2003 and S2004 arethe same as those of the first embodiment.

In step S2005, the anchor eNB 200-1 receives data (DL data) addressed tothe UE 100 from the S-GW 300U via the S1 connection for the UE 100. Theanchor eNB 200-1 determines to start the paging of the UE 100 inresponse to the reception of the data.

In step S2006, the anchor eNB 200-1 transmits, to the eNB 200-2, apaging request requesting implementation of paging (RAN paging) of theUE 100. The paging request may include information for specifying apaging timing (see a third embodiment).

In step S2007, the anchor eNB 200-1 starts a timer when the anchor eNB200-1 determines to start paging or when the anchor eNB 200-1 transmitsa paging request. The anchor eNB 200-1 may stop the timer when theanchor eNB 200-1 receives a paging response from the UE 100 or when theanchor eNB receives a paging success notification from the eNB 200-2.

In step S2008, the anchor eNB 200-1 and the eNB 200-2 transmit a pagingmessage (RAN paging) addressed to the UE 100 within the RAN paging areaconfigured to the UE 100. Here, the description will be given on theassumption that the UE 100 has failed to receive the paging message (Ranpaging).

In step S2009, the eNB 200-2 transmits, to the anchor eNB 200-1, afailure notification (paging failure) indicating that the paging (RANpaging) of the UE 100 has failed.

In step S2010, the anchor eNB 200-1 determines whether the timer hasexpired and/or whether the failure notification (paging failure) hasbeen received. Here, the description will be given on the assumptionthat the timer has expired and/or the failure notification (pagingfailure) has been received.

In step S2011, the anchor eNB 200-1 transmits, to the MME 300C, afailure notification (RAN paging failure) indicating the failure of theRAN paging on the S1 interface. The failure notification (RAN pagingfailure) includes an identifier (for example, eNB UE S1AP ID) for theMME 300C to identify the UE 100. The failure notification (RAN pagingfailure) may include an MME UE S1AP ID, a cause (for example, RAN PagingFailed), and the like. Instead of the failure notification (RAN pagingfailure), a paging request that requests execution of paging may beused.

In step S2012, the MME 300C transmits a paging message (PAGING) to eacheNB 200 belonging to the tracking area in which the UE 100 exists, inresponse to the reception of the failure notification (RAN pagingfailure) from the anchor eNB 200-1. Each eNB 200 belonging to thetracking area in which the UE 100 exists transmits the correspondingpaging message to its own cell. However, instead of transmitting thepaging message to all the eNBs 200 belonging to the tracking area inwhich the UE 100 exists, the MME 300C may transmit the paging messageonly to a part of the eNBs 200 belonging to the tracking area.

In step S2013, in response to the reception of the paging message(PAGING), the UE 100 transmits, to the eNB 200 (for example, the anchoreNB 200-1), a message (RRC connection boot request) requesting theresume from the light connected state.

Third Embodiment

In a third embodiment, a difference from the first and secondembodiments will be mainly described below. The third embodiment is anembodiment related to the DRX operation of the UE 100 in the lightconnected state.

First, a general idle mode DRX operation will be described. In order toreduce power consumption, discontinuous reception (DRX) may beconfigured to the UE 100. In the DRX operation, the UE 100 in the RRCidle mode monitors a paging message in paging occasion occurring at apredetermined time interval (DRX cycle). In the DRX operation, the UE100 intermittently monitors the PDCCH so as to receive paging. The UE100 decodes the PDCCH by using a paging identifier (P-RNTI: paging radionetwork temporary identifier) and acquires paging channel allocationinformation. The UE 100 acquires a paging message based on theallocation information. A PDCCH monitoring timing in the UE 100 isdetermined based on an identifier (IMSI: international mobile subscriberidentity) of the UE 100. The PDCCH monitoring timing (PDCCH monitoringsubframe) in the DRX operation is referred to as paging occasion (PO).The PO corresponds to paging reception occasion.

The UE 100 and the eNB 200 calculate paging occasion (PO) and a pagingframe (PF) that is a radio frame including paging occasion as follows.

A system frame number (SFN) of PF is obtained from the following Formula(1).

SFN mod T=(T div N)*(UE+ID mod N)  (1)

However, it should be noted that T is the DRX cycle of the UE 100 formonitoring paging and is expressed by the number of radio frames. Inaddition, T is the smaller one of a default DRX value the eNB 200broadcasts by a system information block (SIB) and a UE-specific DRXvalue configured to the UE 100 by the NAS message. If the UE-specificDRX value is not configured, the UE 100 applies the default DRX value.In addition, N is the minimum value of T and nB. nB is a value selectedfrom 4T, 2T, T, T/2, T/4, T/8, T/16, and T/32. UE_ID is a value obtainedfrom “IMSI mod 1024”.

Among PFs thus obtained, the index i_s is obtained by the followingFormula (2) and the subframe number of the PO corresponding to the indexi_s is obtained.

i_s=floor(UE_ID/N)mod Ns  (2)

However, Ns is the maximum value from among 1 and nB/T.

Next, an operation according to a third embodiment will be described.FIG. 12 is a diagram illustrating an operation according to the thirdembodiment.

The UE 100 according to the operation pattern 1 of the third embodimentincludes a receiver 110 that receives, from a serving cell, a transitioninstruction instructing a transition to a light connected state, and acontroller 130 that transitions to the light connected state in theserving cell and performs a DRX operation of an RRC connected mode. Thatis, as illustrated in FIG. 12(a), the UE 100 continues the DRX operationof the RRC connected mode while the UE 100 exists in the serving cell atthe time point of the transition to the light connected state. Asillustrated in FIG. 12(b), the controller 130 of the UE 100 stops theDRX operation of the RRC connected mode in response to the UE 100'smoving from the serving cell to another cell in the RAN paging area. Thecontroller 130 of the UE 100 stops the DRX operation of the RRCconnected mode and starts the operation based on the DRX operation ofthe RRC idle mode. The operation based on the DRX operation of the RRCidle mode is an operation of determining PF and PO by a calculationformula of a paging frame (PF) and a paging occasion (PO) in a DRXoperation of the RRC idle mode or a calculation formula that diverts thesame. As illustrated in FIG. 12(c), the controller 130 of the UE 100performs notification when the UE 100 moves to a different RAN pagingarea.

Alternatively, even when the UE 100 moves from the serving cell at thetime of the transition to the light connected state to another cell, ifthe another cell belongs to the same RAN paging area, the UE 100according to the operation pattern 2 of the third embodiment continuesthe DRX operation of the RRC connected mode. In this case, asillustrated in FIGS. 12(a) and 12(b), the UE 100 can continue the DRXoperation of the RRC connected mode within the same RAN paging area.That is, even if the UE 100 moves to another cell, the UE 100 performs areceiving operation according to the connected mode DRX. As describedlater, in the paging request, the configuration value (DRX Config) ofthe connected mode DRX may be transferred to the eNB 200-2.

Here, such an operation may be performed in units of eNBs 200. That is,in the operation patterns 1 and 2 of the third embodiment, the “servingcell” may be read as “serving eNB” or “anchor eNB”, and the “other cell”may be read as “another eNB”.

In the operation patterns 1 and 2 of the third embodiment, the UE 100other than the anchor eNB does not necessarily hold the contextinformation of the UE 100. Therefore, it is desirable for the anothereNBs within the same RAN paging area to acquire, from the anchor eNB,information for determining the timing of the paging.

The eNB 200-2 (see FIG. 11) according to the third embodiment includes acontroller 230 that performs RAN paging on the UE 100 in the lightconnected state. The controller 230 acquires, from the anchor eNB 200-1(see FIG. 11), information for determining the timing of transmittingthe paging message for RAN paging to the UE 100. The information fordetermining the timing includes at least one of the identificationinformation (for example, IMSI, S-TMSI, resume ID, and the like) of theUE 100 and the DRX configuration of the RRC connected mode. The anchoreNB 200-1 may include such information in the paging request andtransmit the information to the eNB 200-2 (see step S2006 in FIG. 11).

In the third embodiment, the identification information for determiningthe timing of the paging may be an E-UTRAN cell global identifier (ECGI)and a cell-radio. network temporary identifier (C-RNTI). If the UE 100transitions to the light connected state, the anchor eNB 200-1 mayallocate the identification information to the UE 100.

Fourth Embodiment

In a fourth embodiment, a difference from the first to third embodimentswill be described below. The fourth embodiment is an embodiment relatedto a message for transitioning the UE 100 to the light connected state.

FIG. 13 is a diagram illustrating the operation pattern 1 of the fourthembodiment. In the operation pattern 1 of the fourth embodiment, the UE100 includes a receiver 110 that receives an RRC connectionreconfiguration message from the serving cell, a transmitter 120 thattransmits, to the serving cell, an RRC connection reconfigurationcomplete message, which is a response message to the RRC connectionreconfiguration message, in response to the fact that the transitioninstruction instructing the transition to the light connected state isnot included in the RRC connection reconfiguration message, and acontroller 130 that stops the transmission of the RRC connectionreconfiguration complete message in response to the fact that thetransition instruction is included in the RRC connection reconfigurationmessage. Here, the transition instruction may be configurationinformation related to light connection. According to the operationpattern 1, the UE 100 does not transmit the RRC connectionreconfiguration complete message if the light connection is set up inthe RRC connection reconfiguration. Therefore, signaling can be reduced.

FIG. 14 is a diagram illustrating the operation pattern 2 of the fourthembodiment. In the operation pattern 2 of the fourth embodiment, the UE100 includes a receiver 110 that receives an RRC connection releasemessage from the serving cell, a controller 130 that stops thetransmission of the response message to the RRC connection releasemessage in response to the fact that the transition instructioninstructing the transition to the light connected state is not includedin the RRC connection release message, and a transmitter 120 thattransmits an RRC connection release complete message to the serving cellas a response message in response to the fact that the transitioninstruction is included in the RRC connection release message. Here, thetransition instruction may be configuration information related to lightconnection. The controller 130 of the UE 100 transitions to the lightconnected state when confirming that the RRC connection release completemessage has been delivered based on, for example, HARQ ACK. According tothe operation pattern 2, the UE 100 transmits an RRC connection releasecomplete message if the transition to the light connected state isinstructed in the RRC connection release. Therefore, the eNB 200 canmore reliably confirm that the UE 100 has transitioned to the lightconnected state.

Fifth Embodiment

In a fifth embodiment, a difference from the first to fourth embodimentswill be described below. The fifth embodiment is an embodiment relatedto a message for the UE 100 to resume from the light connected state.

The UE 100 according to the fifth embodiment includes a transmitter 120that transmits, to the serving cell, information indicating the resumefrom the light connected state, and a controller 130 that resumes fromthe light connected state without receiving the RRC connectionreconfiguration message from the serving cell. The informationindicating the resume from the light connected state is, for example,the above-described RRC activation request, RRC connection resumerequest, RRC connection boot request, or the like.

FIG. 15 is a diagram illustrating the operation example according to thefifth embodiment.

As illustrated in FIG. 15, according to a conventional approach (legacyapproach), the UE 100 in the light connected state transmits, to the eNB200, a request for resuming from the light connected state. Next, the UE100 receives an RRC connection reconfiguration message from the eNB 200and transmits an RRC connection reconfiguration complete message to theeNB 200, thereby resuming from the light connected state (transitioningto the RRC connected mode).

As illustrated in FIG. 15(b), according to the first approach (one-stepapproach) of the fifth embodiment, the UE 100 in the light connectedstate merely transmits, to the eNB 200, a notification (Indication)indicating the resume from the light connected state, thereby resumingfrom the light connected state (transitioning to the RRC connectedmode). The notification (indication) may include information requestingallocation of radio resources (scheduling request) and/or informationreporting an uplink buffer status (buffer status report). If it cannotbe confirmed based on HARQ ACK or the like that the notification(Indication) has been delivered, the UE 100 may maintain the lightconnected state or may transition to the RRC idle mode.

As illustrated in FIG. 15(c), according to the second approach (two-stepapproach) of the fifth embodiment, the UE 100 in the light connectedstate transmits, to the eNB 200, a request for resuming from the lightconnected state and merely receives an acknowledgment for the requestfrom the eNB 200, thereby resuming from the light connected state(transitioning to the RRC connected mode). The request may includeinformation requesting allocation of radio resources (schedulingrequest) and/or information reporting an uplink buffer status (bufferstatus report). The eNB 200 may transmit a non-acknowledgment to the UE100 in response to the request. If the UE 100 receives thenon-acknowledgment, the UE 100 may maintain the light connected state ormay transition to the RRC idle mode. Whether to maintain the lightconnected state or transition to the RRC idle mode may be designated bythe non-acknowledgment.

Therefore, according to the fifth embodiment, signaling can be reducedas compared with the conventional approach. The reasons why the RRCconnection reconfiguration is unnecessary include the following causes.Specifically, assuming that the light connected state is similar to theRRC connected mode, the eNB 200 does not need to prepare a new resource(that is, there is no reason for rejection). In addition, there is noneed for the UE to newly apply the configuration (that is, there is noconfiguration failure). Furthermore, there is no RRC state transition,and it is not necessary for the eNB 200 and the UE 100 to recognize eachother. For example, if the UE 100 is operating according to the DRX ofthe RRC connected mode, since the reception timing of the UE 100 is thesame in both the light connected state and the RRC connected mode, datacommunication is not established.

However, the UE 100 may perform the operation according to the fifthembodiment only when the UE 100 exists in a cell at the time point ofthe transition to the light connected state. If the UE 100 moves fromthe cell at the time of the transition to the light connected state toanother cell in the same RAN paging area, the UE 100 may perform theoperation according to the conventional approach.

The notification (indication) and the request according to the fifthembodiment may be transmitted to the eNB 200 during a random accessprocedure. As an example, the notification (indication) and the requestmay be transmitted from the UE 100 to the eNB 200 during Msg 1 (randomaccess preamble/PRACH transmission) or Msg3 (scheduled transmission) ofthe random access procedure. In addition, the acknowledge or thenon-acknowledgment may be transmitted from the eNB 200 to the UE 100during Msg2 (random access response) or Msg4 (contention resolution) ofthe random access procedure.

Sixth Embodiment

In a sixth embodiment, a difference from the first to fifth embodimentswill be described below. The sixth embodiment is an embodiment relatedto a notification (extended PPI) indicating interruption of datacommunication.

As described above, the UE 100 transmits a notification (extended PPI)to the eNB 200 if data communication does not occur (or there is nopossibility of occurrence). On the other hand, in the sixth embodiment,the notification (extended PPI) is improved as follows.

The UE 100 according to the sixth embodiment includes a controller 130that detects interruption of data communication with the serving cell(eNB 200), and a transmitter 120 that transmits, to the serving cell, anotification (extended PPI) indicating the interruption of the datacommunication in response to the detection of the interruption (datainactive) of the data communication. The controller 130 estimates theexpected time of the interruption of the data communication. Thetransmitter 120 transmits the notification (extended PPI) including theexpected time.

The UE 100 (controller 130) may estimate the interruption time of thedata communication according to information from the application layeras described above. Specifically, the time notified from the applicationlayer may be the expected time as it is. Alternatively, It may beexpected on the UE 100 (AS side) by using information such as whichapplication is activated from the application layer and whichapplication is shut down, or information such as whether the user iscurrently performing an operation (or whether foreground communicationis assumed or only background communication is assumed). The accessstratum (AS) includes each protocol below the RRC layer. For example,the traffic generation pattern is preliminarily collected on the ASside, the traffic prediction is performed, and the predicted time isestimated while using information from the application layer and thelike as needed.

In the sixth embodiment, the notification (extended PPI) may be a directnotification that it wants to enter the light connected state or adirect notification that it is possible to enter the light connectedstate.

In the sixth embodiment, the eNB 200 may explicitly or implicitlyconfigure, to the UE 100, whether to transmit the notification (extendedPPI). For example, if an identifier indicating the permission of thetransmission of the notification (extended PPI) is informed to SIB, orif the eNB 200 configures (setup) the transmission of the notification(extended PPI), the UE 100 determines that the transmission of thenotification (extended PPI) is permitted. In addition, 1) whether thenotification (extended PPI) is determined by the past state (that is,data is not generated), 2) whether the notification (extended PPI) isdetermined by the future expectation (that is, there is no possibilityof occurrence), and 3) whether the notification (extended PPI) isdetermined by including both the past and the future may be configuredfrom the eNB 200 to the UE 100. Furthermore, a prohibit timer valueand/or a report period of the notification (extended PPI) may beconfigured from the eNB 200 to the UE 100. The prohibit timer is a timerthat specifies the time until the UE 100 can transmit the nextnotification (extended PPI) after transmitting the notification(extended PPI).

In the sixth embodiment, the notification (extended PPI) may include arecommended cycle or a desired DRX cycle of DRX for light connection.The UE 100 (the controller 130) may determine a desired value of the DRXcycle based on the above-described expected time of the interruption ofthe data communication. Specifically, the UE 100 determines anappropriate DRX cycle based on its own situation and transmits the DRXcycle during the notification (extended PPI). The UE 100 may apply thenotified DRX cycle when the notification is performed. Alternatively,the UE 100 may configure the DRX cycle according to the response (suchas RRC connection reconfiguration) by the eNB 200. In the case ofapplying the DRX cycle by performing the notification, it may beregarded as transitioning to Light Connected with this application.

It should be noted that the eNB 200 may configure (for example,broadcast or unicast) the timer value to the UE 100 until transitioningto Light Connected. The UE 100 resets (restarts) the timer when datacommunication is performed, and transitions to Light Connected when thetimer expires. The UE 100 may notify the eNB 200 of the datainterruption when the data communication is interrupted (for example,when the expected time is after the timer expires) while the timer isoperating.

Seventh Embodiment

In a seventh embodiment, a difference from the first to sixthembodiments will be described below. The seventh embodiment is anembodiment related to the cell reselection operation of the UE 100 inthe light connected state.

The UE 100 according to the seventh embodiment includes a controller 130that performs the cell reselection operation in the light connectedstate. In the cell reselection operation, the controller 130preferentially selects a cell that supports a resume from the lightconnected state as a serving cell of the UE 100.

A general cell reselection operation is an operation of selecting anappropriate cell according to a ranking based on the priority of thefrequency to which the cell belongs and the radio quality of the cell.

In the cell reselection operation according to the seventh embodiment,the UE 100 (controller 130) may set the cell that supports LightConnected as the highest priority. The UE 100 (controller 130) may setthe cell that does not support Light Connected as the lowest priority.Here, highest./lowest means the priority (for example, “8”, “−1”)higher/lower than the priority (CellReselectionPriority: 0 to 7)broadcasted from the eNB 200 or a value obtained by adding the priorityand subpriority (CellReselectionSubPriority: 0.2, 0.4, 0.6, 0.8).

Alternatively, in the cell reselection operation according to theseventh embodiment, the UE 100 (controller 130) may prioritize the cellthat supports Light Connected by introducing an offset into the ranking.For example, a positive offset is added to the cell that supports LightConnected and/or a negative offset is added to the cell that does notsupport Light Connected. The offset value may be a predefined value or avalue set from the eNB 200. If the offset value is set from the eNB 200,the eNB 200 may broadcast the offset value, or may set the offset valueby UE-specific dedicated signaling.

In the seventh embodiment, the eNB 200 may configure, to the UE 100,whether to perform priority control of cells supporting the resume fromthe light connected state. The configuration may be configured whentransitioning to the light connected state. The configuration may beincluded in the RRC connection reconfiguration or the RRC connectionrelease.

Each eNB 200 (each cell) may broadcast information indicating whetherthe light connected state (specifically, the resume from the lightconnected state) is supported. As an example, the eNB 200 transmits theinformation by SIB. Such information may be implicit information. Forexample, the UE 100 may regard the cell transmitting the identifier ofthe RAN paging area as the cell supporting the light connected state.

In the seventh embodiment, the UE 100 may transition to the RRC idlemode in response to no detection of the cell that supports the resumefrom the light connected state and satisfies a predetermined radioquality criterion (for example, S criterion). As an example, the UE 100may transition to the RRC idle mode if the cell that satisfies Scriterion is only the legacy cell (that is, the cell that does notsupport the light connected state).

Other Embodiments

The present disclosure is not limited to the case in which theabove-described embodiments are separately and independently performed,but two or more embodiments may be performed in combination. Forexample, a part of operations according to one embodiment may be addedto other embodiments. Alternatively, a part of operations according toone embodiment may be replaced with a part of operations of otherembodiments.

In the above embodiment, the case in which the UE 100 receivesmultimedia broadcast multicast service (MBMS) or is interested inreceiving multimedia broadcast multicast service (MBMS) has not beenparticularly mentioned. However, the eNB 200 may determine whether totransition the UE 100 to Light Connected based on the reception statusor the like of the multimedia broadcast multicast service (MBMS) in theUE 100. As an example, if single-cell point-to-multipoint (SC-PTM)reception is not performed in the light connected state (for example, ifSC-PTM reception is not permitted, if UE capability is insufficient, orthe like), the eNB 200 does not transition the UE 100 to LightConnected. As another example, when interest in MBMS service reception(for example, SC-PTM reception) is indicated in the MBMS interestindication, the eNB 200 does not transition the UE 100 to LightConnected. In addition, some UEs 100 cannot receive the MBMS in the RRCconnected state. If the UE 100 is capable of MBMS reception with LightConnected, the eNB 200 may transition the UE 100 to Light Connected inresponse to the fact that the UE 100 indicates interest in MBMS servicereception (for example, SC-PTM reception).

In addition, in the first embodiment described above, the example inwhich the identifier including the combination of the cell ID and theC-RNTI is included in the paging message has been described.

Meanwhile, even if MT data with high priority (incoming call in the UE100) occurs, there is no means for indicating the situation in thecurrent paging. Therefore, if paging occurs for the UE 100 thatprioritizes MBMS reception (for example, SC-PTM reception), there is apossibility that it cannot appropriately determine whether MBMSreception is continued or whether MBMS reception is interrupted and RRCconnection is prioritized.

Therefore, priority information is assigned to the paging message sothat appropriate determined can be made. The priority information may bea value of establishment cause (for example, high priority access), maybe an identifier indicating that the incoming call has high priority,may be a numerical value (for example, 0 to 7) indicating the priority,or may be a bearer identifier associated with the incoming call. Inaddition, the priority information may be provided by a list, and eachentry of the list may correspond to each entry of a list of UEidentifiers (paging record list) in the paging message. Alternatively,the priority information may be incorporated in the entry (that is,paging record) of the paging record list. The priority information maybe determined by the eNB 200 or may be determined by the MME 300C.

The UE 100 having received the paging message including the priorityinformation determines necessity of an RRC connection start process (forexample, transmission of RRC connection request) by using the priorityinformation. If the RRC connection process is started, the message ofthe RRC connection process may notify to the eNB 200 that it is aprocess based on the priority information (for example, “prioritized MTcall”), and the notification may be included in establishment cause.

On the other hand, if the MBMS reception is prioritized rather than thepaging including the priority information, the UE 100 may not respond tothe paging.

In each of the above-described embodiments, the example in which thelight connected state is terminated with the occurrence of thepredetermined event as a trigger has been described. The light connectedstate may be valid only during a period in which the timer configuredfrom the eNB 200 to the UE 100 is in operation. In this case, thepredetermined event may be the expiration of the timer. Alternatively,the light connected state may be valid only during a period in which theUE 100 exists within a predetermined frequency. For example, the UE 100having received the instruction of the light connected state in acertain cell may terminate the light connected state in response to themovement to a cell having a frequency different from the frequency towhich the cell belongs.

In each embodiment described above, the LTE system has been exemplifiedas the mobile communication system. However, the present disclosure isnot limited to the LTE system. The present disclosure may be applied tosystems other than the LTE system.

(Additional Note 1)

(1. Introduction)

RAN2 #95 agreed the basic functions/characteristics of Light Connectionas follows.

Agreements:

the functions of a lightly connected UE include:

-   -   S1 connection is kept and active in the “anchor eNB”    -   Support of RAN initiated paging    -   The paging process is controlled by “anchor eNB”    -   eNB controlled RAN based paging area    -   RAN based paging area update mechanism. RAN based paging area        can be configurable as UE specific    -   Performing cell reselection based mobility, the same cell        reselection mechanism in RRC IDLE.    -   The UE AS context is kept in both UE and “anchor eNB” side.    -   The ECM state is ECM-CONNECTED, from perspective of network.        From UE perspective the state is FFS.    -   When a “lightly connected” UE is paged (via RAN-initiated        paging) or when any MO data/signaling is triggered, the UE will        get back to be connected to eNB. The related procedure is FFS.    -   A UE enters into “lightly connected” by RRC signaling. The        details are FFS.

In this contribution, the details of Light Connection are discussed.

2. Discussion

(2.1. Modeling Principles)

(2.1.1. RRC States and “Substate”)

LTE has a couple of RRC states, i.e., RRC Connected and RRC IDLE. Evenwhen RRC Connection Suspend/Resume procedure was introduced in Rel-13,it kept the two states modelling. The UE with suspending RRC connectionis just in RRC IDLE from the state point of view, i.e., a “substate” ofIDLE UEs with storing the AS context and the resume ID. The two statesmodelling works well to simplify the state transitions and theseconditions, which were a bit complex in the legacy system. So, RAN2should stick to the RRC modelling even if Light Connected is introduced,i.e., to be defined as Light Connected “substate” which is a part of RRCConnected or

IDLE whereby certain features are added or restricted depending on thedesired operations to be decided by RAN2.

Proposal 1: RAN2 should stick to the existing two states modelling,i.e., RRC Connected and IDLE, when Light Connected is defined in RRC.

(2.1.2. Baseline States)

If Proposal 1 is agreeable, Light Connected “substate” is built on topof either RRC Connected or RRC IDLE.

It was suggested in RAN2 #95 that RRC Suspended/Resume is the baselineof Light Connected. It's indeed a nice way from RAN2 standardizationefforts point of view, that Light Connected is a combination ofsuspending RRC connection from UE's perspective and the new feature tokeep S1 connections in active from CN's perspective. Even though it'sstill beneficial for S1, i.e., eliminating the UE Context Suspend/ResumeRequest/Response, it should be noted that compared to Rel-13 there willbe no gain in Rel-14 in terms of reductions of signalling and latency inUu, since it relies on Rel-13 procedure. Additionally, the ECM statemismatch will happen between the NW and the UE in Light Connected, i.e.,“The ECM state is ECM-CONNECTED, from perspective of network” butECM-IDLE from the UE's perspective since the UE is in RRC IDLE duringRRC Connection is suspended. It's unclear whether the mismatch isacceptable to the other WGs.

Observation 1: RRC Suspend-based Light Connection may be possiblewithout any gain in terms of signalling/latency reduction in Uu.

Observation 2: It's unclear whether the ECM state mismatch between theNW and the UE in Light Connected is acceptable.

On the other hand, RRC Connected-based approach was also proposed.Needless to say, the most significant benefit of RRC Connected is lowaccess latency in MO and MT calls. Potentially, no paging is necessaryfor MT call, although it's already agreed to introduce “Support of RANinitiated paging” for Light Connection. In addition, the ECM-state isnaturally aligned between the NW and the UE. So, RRC Connected-basedLight Connection has the potential to improve the signalling and latencyin Uu, without unnecessary impacts to the higher layer, i.e., NAS.However, it's obviously worse for the UE power consumption just to keepthe UEs in legacy RRC Connected, i.e., it cannot achieve the objectivethat “The solution shall enable the UE power consumption to becomparable to that one in RRC_IDLE”. Therefore, some optimizations wouldbe necessary, if RRC Connected-based Light Connection is the way.

Observation 3: RRC Connected-based Light Connection may have thepotential to improve the signalling overhead and the access latency inUu without unnecessary impacts to the higher layer, although thestandardization efforts will be necessary in RAN2 to minimize the UEpower consumption.

As the first statement of WI objectives stated “The objective of thiswork item is to reduce the radio and network interfaces signallingoverhead, and improve the UE access latency as well as UE powerconsumption for all device types”. The work should consider all devicetypes, i.e., not just MTC UEs, but also normal LTE UEs like smartphones.Regarding MTC type traffic, it was already optimized by RRC ConnectionSuspend/Resume in Rel-13 and it's of course applicable to normal LTEUEs. So, Rel-14 work should rather focus on normal LTE UEs, e.g.,smartphone traffics.

Observation 4: Light Connection should be efficient for not only the MTCtype traffic, which was already optimized in Rel-13, but also the normalLTE traffic like smartphone, which seems to be the primary challenge inRel-14.

Considering the observations above, i.e., ECM state mismatch, furtheroptimization of signalling/latency and adapation for smartphone traffic,RAN2 should take RRC Connected state as the baseline for Light Connected“substate”.

Proposal 2: RAN2 should take RRC Connected state as the baseline forLight Connected.

(2.2. Rrc Signaling)

2.2.1. Entering to Light Connected

RAN2 #95 agreed that “A UE enters into “lightly connected” by RRCsignaling. The details are FFS”. If Proposal 2 is agreeable, it'sstraight forward to use RRC Connection Reconfiguration message for setupof Light Connected, since RRC Connection Release for RRC Connectionsuspension makes the UE transition to RRC IDLE.

Proposal 3: RAN2 should use RRC Connection Reconfiguration message forsetup of Light Connected.

However, one drawback with RRC Connection Reconfiguration message is toperform the handshake with RRC Connection Reconfiguration Complete,while this isn't needed for RRC Connection Release. From the signallingreduction point of view, it is preferable for the UE not to send the RRCConnection Reconfiguration Complete. However, without an acknowledgementsuch as the case with RRC Connection Release message would increase theprobability of state mismatch between the serving cell and the UE. Incontrast, if RRC Connected-based Light Connection is already a substateof RRC Connected state then the issue with mismatch of state transitionwould not be a significant concern. So, RAN2 should discuss whether theRRC Connection Reconfiguration Complete is necessary when the UE goes toLight Connected.

Proposal 4: RAN2 should discuss whether or not an acknowledgement fromthe UE, e.g., RRC Connection Reconfiguration Complete, is necessary whenthe UE goes to Light Connected.

It's also worth considering whether to allow autonomous transition toLight Connected. The serving cell may set the UE with an “inactivity”timer via broadcast/dedicated signalling, and the UE autonomously goesto Light Connected when the timer expires. It could further reduce theoverhead for Light Connected control in Uu.

Proposal 5: RAN2 should discuss whether to allow the autonomous enteringto Light Connected, with e.g., an “inactivity timer”, for furthersignalling reduction.

(2.2.2. Leaving from Light Connected)

It was also agreed that “When a “lightly connected” UE is paged (viaRAN-initiated paging) or when any MO data/signaling is triggered, the UEwill get back to be connected to eNB. The related procedure is FFS”. So,it's worth considering how to return from Light Connected to RRCConnected.

With the legacy approach, the handshake to get RRC Connected needs (atleast) three steps, e.g., (1) RRC Connection Resume Request, (2) RRCConnection Resume and (3) RRC Connection Resume Complete, as illustratedin (a) of FIG. 15. On the other hand, the signalling and latency couldbe reduced if the handshake is minimized, i.e., (b) and (c) in FIG. 1.

The one-step approach, e.g., with an indication from the UE as (b) inFIG. 15, is beneficial to minimize the signalling and latency. Regardingthe state mismatch issue discussed in Proposal 4, from the perspectiveof reachability of messages, only the DL will be an issue mainly due tothe UE's radio problem (i.e., the reception errors during T310 runs,which is seen only in the UE, never in the serving cell). So, theone-step approach is technically feasible.

It could be also considered whether the serving cell needs to reject theUE getting back to RRC Connected, as (c) in FIG. 15. If Proposal 2 isagreeable, i.e., RRC Connected-based “substate”, there seems no need tohave the reject message since the UE in Light Connected is already partof RRC Connected. When the number of RRC Connection needs to be reducedfor some reason, the serving cell may initiate RRC Connection Releaseanytime, as it is today.

So, while the one-step approach is our preference, RAN2 should discusswhether to optimize the signalling during the return from LightConnected to RRC Connected.

Proposal 6: RAN2 should consider to minimize the handshake for returnfrom Light Connected to RRC Connected.

(2.2.3. Awareness of inactivity during RRC Connected) Since “A UE entersinto “lightly connected” by RRC signaling”, the serving cell needs todetermine when to trigger entering Light Connected. One of the possibleimplementation is that the serving cell monitors the traffic behaviourand has the UE to enter Light Connected when the UE's packet is nottransmitted/received for a period. It relies on the expected trafficbehaviour, so if the expectation is not accurate then the signallingoverhead may actually increase, e.g., frequent transitions between LightConnected and RRC Connected, or the chance to entering Light Connectedis missed. While MTC-type traffic is somewhat easily expected, LTE-typetraffic, esp. smartphone's traffic behaviour, may not be as easy for theNW to predict. Therefore, it may be necessary for the UE to provide someassistance information since the UE has a better knowledge/control ofits traffic behaviour. So, it's worth considering whether the servingcell may configure the UE to provide the assistance information for itsdecision to trigger Light Connected.

Proposal 7: RAN2 should discuss whether the serving cell may configurethe UE to provide the assistance information, for the decision of RRCsignalling to make the UE to enter Light Connected.

If Proposal 7 is agreeable, the assistance information may have somesimilarity with the existing Power Preference Indicator (PPI) and/orMBMS Interest Indication (MII). With PPI, the UE may inform oflowPowerConsumption when its power consumption is preferred to beoptimized by e.g., longer DRX cycle. The MII was used to inform of theMBMS frequencies of interest and the priority between Unicast and MBMSe.g., when the handover to the frequency is preferred. In this case, theUE may inform the serving cell of the possibility to enter LightConnection; in other words, the UE may send the assistance informationwhen the data transmission/reception has been/will be inactive incertain duration. The details and necessity of any additional assistanceare FFS, e.g., UE's expected inactive time.

Proposal 8 RAN2 should consider if the UE should send the assistanceinformation upon data inactivity.

(2.3. Activities During Light Connected)

(2.3.1. Paging Monitoring)

RAN2 #95 agreed to support RAN-initiated paging, so the UE needs tomonitor it during Light Connected in the subframes determined “as abaseline that Rel-13 legacy PO/PF calculations are used for theRAN-initiated paging”.

On the other hand, the three scenarios could be considered when the UEreturns to RRC Connected associated with UE mobility, as illustrated inFIG. 12.

Scenario 1: The UE remains in the same cell as where it entered LightConnected.

This scenario may happen often, especially in case of smartphone isassumed. If Light Connection is a part of RRC Connected, i.e., Proposal2, C-RNTI is still active and valid, which could be still reused to pagethe UE. So, the UE may monitor Paging in the occasions determined by theexisting Connected mode DRX (C-DRX).

Scenario 2: The UE is in a different cell within the same RAN pagingarea (PA) where it entered Light Connected.

In the different cell, the C-RNTI is no longer valid since it's acell-specific ID. So, the other ID may be necessary to page the UE, suchas “(a) NAS UE ID (i.e. S-TMSI), (b) Rel-13 UE Resume ID, (c) a new RANUE ID or (d) IMSI mode”. However, the “paging occasion” is stilldetermined by C-DRX if the DRX-Config is transferred to the target celle.g., within “X2 paging”.

Scenario 3: The UE is outside of the RAN paging area where it enteredLight Connected.

In this case, “UE lightly connected is required to notify the network”.The UE may be instructed to be in Light Connected in the cell where thenotification is sent. So this scenario is the same condition withScenario 1 and no further consideration is necessary.

Regarding the paging occasions for the UE in Light Connected, the C-DRXmechanism can be reused even if the UE mobility is taken into account.From RAN2's perspective, no specification impact is foreseen with thisapproach, while the agreement “To take as a baseline that Rel-13 legacyPO/PF calculations are used for the RAN-initiated paging. The inputparameters for PO/PF calculation can be changed if necessary” impliessome impacts and complexity. Therefore, RAN2 should revisit the baselinefor PF/PO calculation.

Proposal 9: RAN2 should decide to reuse the existing Connected mode DRXmechanism, for the paging occasions.

If Proposal 9 is agreeable, the agreement “To define a UE ID for pagingcalculation. Select the UE ID from (a) NAS UE ID (i.e. S-TMSI), (b)Rel-13 UE Resume ID, (c) a new RAN UE ID or (d) IMSI mode” is no longernecessary, since the C-DRX doesn't need to input any IDs to calculate OnDuration.

Proposal 10: If Proposal 9 is agreeable, RAN2 should not use any IDs forcalculation of paging occasions.

Regarding the ID to page the UE, C-RNTI is used in Scenario 1 but not inScenario 2. So, especially for Scenario 2, it's necessary “To define aUE ID conveyed in paging message. Select the UE ID from (a) NAS UE ID(i.e. S-TMSI), (b) Rel-13 UE Resume ID, (c) a new RAN UE ID or (d) IMSImode”. If Light Connected should be transparent to the CN as much aspossible, the ID should be selected form the IDs which can be managed inRAN. So, the candidates are “(b) Rel-13 UE Resume ID” or “(c) a new RANUE ID”. The Resume ID is used for the eNB to retrieve the UE contextfrom “Anchor eNB”, however the exact contents of Resume ID is notvisible to the UE, i.e., only the bit size is defined.

The UE could be identified by an ID which consists of ECGI (i.e.,CellGlobalIdEUTRA in the “anchor eNB”) and C-RNTI (allocated by the cellwith ECGI). To minimize the message size, it could be also considered,instead of ECGI, to use either ECI (i.e., CellIdentity or “eNB ID+PCI”)or PCI (i.e., PhysCellld). With these optimizations, it needs to beassumed that the ID is valid within a PLMN.

If the contents of ID are explicitly specified, the UE would use it todetermine whether it has been paged even if the ID is not explicitlyallocated via RRC signalling, e.g., RRC Connection Reconfiguration orRelease when the UE transitions to Light Connected.

Proposal 11: RAN2 should define “ECGI+C-RNTI”, “ECI+C-RNTI” and/or“PCI+C-RNTI” as the new RAN ID in “paging massage”.

Proposal 12: If Proposal 11 is agreeable, the ID is not necessary to beexplicitly allocated from the cell in “anchor eNB” to the UE when the UEenters Light Connected.

(2.3.2. UE-based mobility) RAN2 agreed that “Performing cell reselectionbased mobility, the same cell reselection mechanism in RRC IDLE”. So,the UE behaviour follows the idle mode procedure, in terms of cellreselection, which seems no problem for the UE in Light Connected aslong as all the eNB in a network support the return from Light Connectedto RRC Connected. Although It may be up to NW implementation, Rel-13didn't assume all eNB in a network supports the new features, e.g.,eDRX-Allowed for eDRX, voiceServiceCauselndication for VoLTEEstablishment Cause, up-CIoT-EPS-Optimisation andcp-CIoT-EPS-Optimisation for RRC Connection Resume and data over NASrespectively. So, it's worth discussion whether it can be assumed thatall eNB in a network support Light Connection.

Proposal 13: RAN2 should discuss whether it can be assumed that all eNBsin a network support Light Connection.

If some eNBs don't support Light Connection, the question is how the UEshould behave, since the UE may become unreachable from RAN paging. Oneof possibilities is that the UE prioritize the cell supporting LightConnected as much as possible. Another possibility is that the UEtransition to RRC IDLE, when it reselects the cell not supporting LightConnected. RAN2 should consider the details of UE-based mobility duringLight Connected.

Proposal 14: If there one or more eNBs do not support Light Connection,RAN2 should discuss the details of UE-based mobility during LightConnected, e.g., whether the cell should be de-prioritized during thecell reselection, and whether the UE should transition to RRC IDLE ifsuch a cell is reselected.

(Additional Note 2)

1. Paging may optionally contains some priority information per UE;

A) The priority information may be;

The values from Establishment Cause, or;

The 1-bit flag to identify that this paging is for prioritized call(e.g., MT voice), or;

The number indicate its MT call priority (e.g., 0-7 like AbsolutePriority for cell reselection), or;

The bearer ID associated with this paging.

The priority information may be formed as a list, and each entry in thelist indicates corresponding entries in PagingRecordList within Paging,or;

The priority information may be integrated within the existingPagingRecord.

C) The priority information may be determined by the eNB (e.g., eVoLTEMT video call case) or by the MME (e.g., via the existing PagingPriority IE in S1 paging).

2. Upon reception of the paging priority in Paging, the UE;

A) May use it to decide whether to initiate RRC Connection Request (orone for Light Connection), i.e., UE implementation, or;

B) Shall initiate RRC Connection Request (or one for Light Connection)if the priority information indicates a high priority call.

The establishment cause in the request may be aligned with the priorityinformation, e.g., “prioritized-MT-call”.

1. A user equipment comprising: a processor and a memory, the processorconfigured to receive from a base station, configuration informationconfiguring the user equipment to provide assistance informationindicating a preference of the user equipment to leave RRC connectedstate, and transmit to the base station, assistance informationindicating that a preferred RRC state of the user equipment is an RRCstate in which an RRC connection is suspended.
 2. The user equipmentaccording to claim 1, wherein the processor is configured to transmitthe assistance information when the user equipment expects not to sendor receive any more data in near future.
 3. The user equipment accordingto claim 1, wherein the processor is configured to start a timer aftertransmitting the assistance information, the timer specifies the timeuntil the user equipment can transmit the assistance information aftertransmitting the assistance information.
 4. An apparatus for controllinga user equipment, the apparatus comprising a processor and a memory, theprocessor configured to receive from a base station, configurationinformation configuring the user equipment to provide assistanceinformation indicating a preference of the user equipment to leave RRCconnected state, and transmit to the base station, assistanceinformation indicating that a preferred RRC state of the user equipmentis an RRC state in which an RRC connection is suspended.
 5. A basestation comprising: a processor and a memory, the processor configuredto transmit to a user equipment, configuration information configuringthe user equipment to provide assistance information indicating apreference of the user equipment to leave RRC connected state, andreceive from the user equipment, assistance information indicating thata preferred RRC state of the user equipment is an RRC state in which anRRC connection is suspended.